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Define metazoa. What are the three theories regarding metazoan ancestry?
- Metazoans are the multicellular organisms that form tissues found in the majority of the animal kingdom.
- Metazoa may have evolved from…
- 1. Syncytial ciliated cells: multinucleated cells that had cilia, such as Paramecium.
- 2. Colonial flagellated cells: flagellated cells that functioned as a colony, such as Volvox.
- 3. Monophyletic: belief that multicellular organisms evolved from a single phylum, and not multiple phyla.
- *#2 is most accepted due to Ribosomal RNA sequencing
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What are the three grades of metazoa? Describe them in detail.
- Mesazoa: a single phylum which is entirely parasitic of invertebrates (octopuses, squids, etc). Minute, ciliated, wormlike with adults called vermiforms (“wormlike”).
- Parazoa: Developed “parallel” to the metazoans; consists of Porifera (sponges) and Placozoa (glide over their food using digestive enzymes).
- Eumetazoa: “True” metazoans; consists of the rest of the animal kingdom
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What are the major clades of bilateral symmetry? Give information about each clade.
- Lophotrochozoans, Ecdysozoa, and Deuterostomia.
- Information about Lophotrochozoans…
- Bilateral symmetry
- Triploblastic
- Protostome (“mouth first”)
- Some develop lophophore (ciliated tentacles or crown for feeding)
- Some have trochophore larva
- 18 phyla that include Platyhelminthes (flatworms), Rotifers, Mollusks (squids, clams, snails), Annelids (earthworms, leeches), Acnthocephala (spiny-headed worms), Nemertea.
- Information about Ecdysozoa…
- Animals that shed a tough external coat/cuticle (eg. Arthropods).
- Process is known as molting or ecdysis
- All invertebrates
- 8 phyla that include Nematoda, Arthropoda, and Onychophora
- Information about Deuterostomia…
- Deuterostome (“mouth second”)
- Phyla include Echinoderms (starfish, no vertebrates), Hemichordata (almost vertebrates), and Chordata (vertebrates)
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Phylum Porifera – Common name? Feeding style? Movement? Habitat? Special cells/structures? Reproduction?
- Sponges
- Filter-feeding through ostia
- Sessile
- Aquatic
- Have many holes on surface (ostia)
- Contain spicules made of Calcium Carbonate, silica, and spongin
- Perform asexual reproduction (budding) and sexual reproduction (sperm and eggs)
- Radial symmetry or no symmetry
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How are sponges classified? What are the three classes of Porifera, and what are their characteristics in detail + genera?
- Classified based on types of spicules, shape of sponge, and DNA. NOT BY CANAL TYPES!
- Calcarea: have calcareous spicules (calcium carbonate) which have 3-4 rays. Have tubular or vase shape. Can have asconoid, syconoid, or leuconoid canal system. (Leucosolenia, Scypha)
- Hexactinellida: “glass sponges” have six-rayed siliceous spicules (silicon) (Euplectella aspergillum)
- Demospongiae: “bath sponges” or “horny sponges.” Skeleton of siliceous spicules (silicon), except bath sponges which have spongin (collagen – a protein) instead. Large sponges that have only leuconoid canal system due to size and complexity. Gemmules are released through osculum, and will become a new sponge. (Spongilla, Chalina, Euspongia)
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Describe basic filter feeding in a sponge (not a specific canal system).
- 1. Water enters through ostia (pores on sides of sponge)
- 2. Microvilli of choanocytes absorb nutrients from water
- 3. Choanocytes transfer nutrients to Amebocytes
- 4. Amebocytes phagocytes nutrient, create spicules
- 5. Flagella of choaocytes push water out
- 6. Water exits through osculum (large hole at top of sponge)
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Describe the various cells and structures found in a sponge.
- Amebocyte (Archaeocyte): amoeba-like cells at the base of each choanocyte. Phagocytizes the food transferred from Choanocytes, creates spicules.
- Spicules: embedded into sponge walls to support sponge structure
- Spongocoel: cavity within the sponge
- Porocytes: cells at the tip of ostium that have the ability to close the ostium when the sponge is in danger (eg. Water is poisoned)
- Pinacocyte: cells on outer surface of sponge which help to regulate surface area (look like squamous epithelial cells)
- Choanocytes (collar cells): cells that absorb nutrients from water (via microvilli) and transfer to Amebocytes. Push water out of the osculum (via flagella)
- Mesoglea (Mesohyl or Mesenchyme): gelatinous area found between pinacocytes and choanocytes
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Describe the three types of canals for sponges and the path of water for each.
- Asconoids: flagellated spongocoel, simplest canal system (eg. Leucosolenia)
- Ostium -> spongocoel (lined with choanocytes) -> osculum
- Syconoids: flagellated canals, moderate canal system (eg. Scypha, Grantia)
- Ostium -> incurrent canal -> prosopyle -> radial canal (containing choanocytes) -> apopyle -> spongocoel -> osculum
- Leuconoids: flagellated chambers, complex canal system. All freshwater and most marine sponges. (eg. Bath sponge)
- Ostium -> incurrent canal -> flagellated chamber (lined with choanocytes) -> excurrent canal -> osculum
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What are the cells that can be found in the mesoglea of a sponge?
- Also known as Mesohyl or Mesenchyme
- Pinacocytes: Half of cell is in mesoglea
- Choanocytes: bulb portion is in mesoglea
- Amebocytes: entirely in mesoglea
- Spicules: entirely in mesoglea
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Types of amebocytes with function.
- Sclerocytes: secrete spicules
- Spongocytes: secrete spongin
- Collencytes: secrete collagen
- Lophocytes: secrete large amount of collagen
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Information about reproduction in sponges
- Asexual: budding and regeneration
- Gemmules are internal buds, released through osculum
- Sexual reproduction: monoecious (hermaphroditic)
- Sperm and oocysts formed from choanocytes
- Some are viviparous
- Some are Oviparous
- NONE are Ovoviviparous
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Viviparous vs. oviparous vs. ovoviviparous
- Viviparous: embryonic development within animal then give birth (mammals)
- Oviparous: lay eggs that require an incubation period (bird)
- Ovoviviparous: lay eggs that hatch immediately, incubation has already taken place inside animal (scorpion, shark)
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